The great majority of residential carpets sold in the United States use synthetic polymeric pile yarns in a construction known as saxony. Two or more nylon, polyester, or polypropylene crimped "singles" yarns are twisted together and set in the ply-twisted configuration either in saturated steam or in dry heat, and such twisted yarns are tufted into a primary carpet backing and cut to form a cut-pile. The carpet is then dyed in an aqueous bath near 100.degree. C. or on a continuous dye range, rinsed and dried. A latex adhesive is applied to the underside of all tufted carpets to retain the tufts in position, and the tufts are then sheared to a uniform pile height.
Cut-pile saxony carpets made from synthetic fibers have excellent bulk and durability versus similar carpets made from natural fibers such as wool. Carpet yarns comprised of synthetic fibers typically have higher bulk than carpet yarns comprised of natural fibers, making it possible to produce carpets from synthetic fibers having higher bulk at lower face weight than carpets made from natural fibers.
In a new cut-pile saxony carpet, each ply-twisted yarn is seen as an individual tuft, and the tufts are said to have "pencil point" or "pin point" definition. However, as the carpet becomes worn, the plied yarn components begin to untwist and the individual filaments in each yarn separate from the bundle and intermingle with those from neighboring tufts. As this process progresses, the tufts are no longer seen as individuals and the surface of the carpet takes on a matted appearance. The contrast between a high-traffic, matted portion of a carpet and a low-traffic portion (near furniture, for example) which has retained its tuft definition, becomes undesirable. Therefore, appearance or newness retention is a carpet property on which consumers place considerable value in that carpets with poor wear properties must be replaced more frequently.
Several methods for improving the wear properties of carpets have been disclosed in the art. Hatt U.S. Pat. No. 3,900,623 describes carpets having a cut-pile in which the filaments in the tufts become unwound and entangled at the tips to form strong coherent tufts. Wilkie & Talley U.S. Pat. Nos. 4,839,211 and 4,882,222 disclose saxony carpets made from blends of conventional and high shrinkage fibers which have improved appearance retention properties when compared to saxony carpets of the same construction without the high shrinkage fibers. The use of heat-activated binder fibers in carpet yarns to improve retention of tuft identity is disclosed in the published patent applications Sekiya JP Kokai 60-224,831, Hackler PCT-WO 88/03969, and Watt & Fowler GB 2205116-A. The binder fibers melt during twist-setting or latexing operations and bond the filaments of the yarn together, resulting in improved twist retention and enhanced wear properties. Hackler, U.S. Pat. No. 4,871,604 describes carpets in which the pile yarn has been coated with a heat-activated binder fiber powder resulting in improved wear performance. Binder fibers and binder powders, however, tend to give the finished carpet an undesirably harsh hand.
Appearance retention and bulk in conventional cut-pile carpets are related to various yarn properties and carpet construction parameters, the most important of these being the yarn modification ratio, yarn bulk, denier per filament (dpf), total yarn denier, degree of ply twist, carpet pile height and pile weight. Other variables that may affect carpet appearance retention include dyeing method, heatsetting method, type of backing, and whether or not padding is used under the installed carpet. Hollow-filament yarns of rectangular-shaped cross-sections which have yarn bulk values as high as 30-35 are made and used for commercial carpet constructions which are characterized by having high pile densities (greater than 4000 oz/yd.sup.3), where pile density is calculated by dividing the weight of the carpet in ounces per square yard by the pile height measured in inches, and multiplying by 36. Such yarns are not suitable for cut-pile residential carpets, however, where pile densities are typically much lower (less than 3600 oz/yd.sup.3). Yarn bulk values (% bulk crimp elongation, as measured and described hereinafter) for trilobal cross-section yarns used in residential cut-pile carpets have not exceeded 20-25 because, typically, initial appearance is poor and as yarn bulk or carpet bulk increases, newness retention decreases. For these reasons, no effort has been made to produce yarns having extremely high bulk values which are suitable for use in residential cut-pile carpets.
One method for improving newness retention is to increase ply twist levels. However, with current carpet yarns, increasing the ply twist to high levels results in a significant reduction in carpet bulk, giving the carpet a "lean" appearance and undesirable hand, thus requiring significantly increased pile weight in order to obtain an aesthetically acceptable carpet.
The current invention provides carpet yarns having new levels of high bulk which when ply-twisted at high twist levels and tufted into cut-pile saxony carpets yield carpets having an improved balance of bulk and appearance retention versus prior art carpets of equal carpet construction. While addition of high twist is known to reduce carpet bulk and improve appearance retention proportionately, we have found that high bulk yarns, while they also lose bulk and gain newness retention upon twisting, achieve a better balance of bulk and newness retention than lower bulk conventional yarns. Thus, the current invention involves carpet yarns having new, high levels of bulk ply-twisted together at unusually high twist levels. Carpets tufted from such yarns surprisingly exhibit an improved and high level of newness retention and bulk when compared with carpets of equal construction made with yarns of conventional bulk and twist levels.